Many high speed packet access (HSPA) evolution features have been introduced in 3GPP since 3GPP Release 7, which increase the sending signalling data rate as well as reducing the signalling delay. Enhanced CELL_FACH in Release 7 was introduced for the downlink to allow a mobile station or user equipment (UE) to support high speed downlink packet access (HSDPA) in CELL_FACH state, and which enables the UE to receive common and dedicated channel data on the HS-DSCH in a non CELL_DCH state. Enhanced Uplink in CELL_FACH and CELL_PCH was introduced in 3GPP Release 8 for the uplink in order to allow the UE to support E-DCH in a CELL_FACH (and a CELL_PCH) state; i.e. the UE can send data over E-DCH instead of the RACH.
Nowadays, more mobile stations support Enhanced CELL_FACH and Enhanced Uplink in CELL_FACH and CELL_PCH features. If the Enhanced CELL_FACH/Enhanced Uplink in CELL_FACH and CELL_PCH features are enabled in a network and supported by mobile stations accessing the network, these mobile stations in IDLE mode or a non CELL_DCH state use Enhanced Uplink in CELL_FACH and CELL_PCH to access the network instead of legacy 3GPP Release 99 access (RACH), when a service is initiated.
However, overloading can occur if too many mobile stations use the Enhanced Uplink in CELL_FACH and CELL_PCH to access the network.